1. Field of the Invention
The present invention relates to intermediates for synthesizing BH.sub.4 and its derivatives, as well as to a process for the preparation of L-biopterin.
2. Related Arts
The compound BH.sub.4, namely, 5,6,7,8-tetrahydro-L-erythrobiopterin, is one of the coenzymes of aromatic amino acid hydroxylase, is an indispensable compound for biosynthesis of dopamine, noradrenalin, adrenaline, and melatonin, and is reprsented by the following formula: ##STR2##
A deficiency of BH.sub.4 causes serious neurological disorders like atypical phenylketonuria and Parkinsonism: and recently, it has been found that symptoms due to such diseases can be remarkably improved by administration of BH.sub.4. Further, it has been recognized that BH.sub.4 is effective for curing infantile autism and depressions.
Since BH.sub.4 has such useful pharmacological activities, various studies have been made for the synthesis thereof, and are referenced as follows: E. L. Patterson et al. "J. Am. Chem. Soc." Vol. 78, page 5868 (1956); H. Rembold et al. "Chem. Ber." Vol. 96, page 1395 (1963); E. C. Taylor et al. "J. Am. Chem. Soc." Vol. 98, page 2301 (1976); M. Viscontini et al. "Helv. Chim. Acta" Vol. 52, page 1225 (1969); ibid., Vol. 55, page 574 (1972); ibid., Vol. 60, page 211 (1977); ibid., Vol 62, page 2577 (1979); K. J. M. Andrews et al. "J. Chem. Soc." (c), page 928 (1969); S. Matsurra et al. "Bull. Chem. Soc. Jpn." Vol. 48, page 3767 (1975); ibid., Vol. 52, page 181 (1979); "Chem. Lett." page 735 (1984); Jap. Pat. No. 59-21685(A); ibid., 59-82091(A); and ibid., 60-204786(A).
Each of the conventional processes for preparing BH.sub.4 has several drawbacks in that an expensive saccharide is required as starting material to provide the asymmetric carbon atom at its side-chain, that yield and purity will become low due to multi-reaction steps, through unstable intermediates that require troublesome treatment operations, and that it requires troublesome purification procedures. Therefore, the conventional processes are unsuitable for industrial production of the compound and its derivatives.